In communication using a spread spectrum signal, the phase of a spread code used for the spread spectrum is regularly initialized (spread code initialization). In spread code initialization, in a system in which the period of spread code initialization and the period of the spread code are not synchronized with each other, it is necessary to perform initialization in the middle of the period of the spread code. Therefore, it is necessary for a receiving side to detect a timing at which initialization of the phase of the spread code is performed (an initialization timing) on a transmitting side, and to perform initialization synchronized with the detected initialization timing. As a method for achieving this synchronization, there is a method that determines whether the initialization timing has come close within the time of one period of the spread code for every period of the spread code on the receiving side; and that, when it is detected that the initialization timing has come close within the time of one period of the spread code, initializes a phase of the spread code at a timing of a specific phase of the spread code within the detected one period (Patent Literature 1).